1. Technical Field
This invention relates to a fixing device for heating, pressurizing, and fixing an unfixed toner image, used with an electrophotographic-type image forming apparatus such as a copier, a printer or a facsimile and in particular to a belt fixing device of an electromagnetic (magnetic) induction heating system and an image forming apparatus using the belt fixing device.
2. Description of the Related Art
Hitherto, in an electrophotographic-type image forming apparatus such as a copier or a printer, for example, a photosensitive member formed like a drum (photosensitive drum) is uniformly charged and is exposed to light, which is controlled based on image information, so as to form an electrostatic latent image on the photosensitive drum. After the electrostatic latent image is formed into a visible image (toner image) with toner and the toner image is transferred from the photosensitive drum directly to a recording medium or after the toner image is once primarily transferred to an intermediate transfer body and is secondarily transferred from the intermediate transfer body to a recording medium, a fixing device fixes the toner image onto the recording medium.
A fixing device of a heating roller system is widely used as a fixing device used in such an image forming apparatus.
In addition to such a heating roll system, a fixing device of an electromagnetic induction heating system has also been known.
In the fixing device of an electromagnetic induction heating system, a roller or a thin fixing belt with a metal layer is used as a fixing member to be heated. When the thin fixing belt is used as the fixing member, the fixing belt can be warmed up in an extremely short time.
The main factor of determining the life of the fixing device of the electromagnetic induction heating system using the fixing belt as described above is a metal layer of a heat generation layer. Generally, since the heat generation layer subjected to electromagnetic induction heating is made of metal, the metal is fatigue-broken because of repeated deformation in the nip portion. As a result, the metal layer does not serve the function as the heat generation layer. This point in time leads to the end of the life of the fixing device of the electromagnetic induction heating system using the fixing belt.
An effective life detection method has not yet been developed for the fixing device of the electromagnetic induction heating system.